The invention described here may be made, used and licensed by and for governmental purposes without paying me any royalty.
1. Field of the Invention
In one aspect this invention relates to armored vehicles. In a further aspect this invention relates to a transparent armor structure useful in military and security vehicles. In yet a further aspect, this invention relates to architectural structures for security purposes.
2. Prior Art
Security has become increasingly important. With respective to vehicle structures in general, military vehicles require greater than average protection for the occupants. This has given rise to various transparent armor structures for windshields and side windows that are designed to resist the incursion of small arms projectiles and shrapnel. This work has been ongoing for many years. In constructing transparent armor, xe2x80x9cbullet proof glassxe2x80x9d, sandwiches made from tempered glass, and plastic layers are bonded together to form complex laminated composites all the. The resulting composites must be transparent and free of optical distortion while maximizing the ballistic protection from penetrators. In use, the inner and out of layers of the composite will be subjected to shock, scratching, abrasion and adverse weather conditions, particularly when a transparent armor composite is used in military applications.
The various layers used in the composite are chosen for their different projectile resisting characteristics and functions. For example, glass layers are hard and thus readily erode bullets and are highly abrasion resistant. However, glass layers are brittle which causes any glass layers opposite a penetration threat to spall, which in turn creates shrapnel fragments. The shrapnel creates numerous projectiles upon the interior surface of the vehicle and the resulting spall or fragments can be more dangerous than the original penetrator. Plastic material layers used as part of a composite sandwich provide a means to introduce flexibility into the transparent armor composite. The addition of one more plastic layers to the composite changes the failure mode of the transparent armor so it fails in a more ductile manner rather than spalling. Acrylic, polyurethane and polycarbonate based materials are among the polymeric materials which have been shown to have utility in making transparent armor composites.
One example of a transparent sheet composite useful as transparent armor is shown in U.S. Pat. No. 5,506,051. This particular patent discloses a laminated glass and polycarbonate construction with the addition of one or more transition layers of cured aliphatic urethane. The urethane provides a tension absorbing transmission layer within the composite. This patent also describes glasses and plastic materials useful in forming laminates that can be used as transparent armor.
One class of plastics that has proven both useful and reliable in constructing transparent armor composites and architectural bandit type barriers is polycarbonate. Polycarbonate has proved to have superior characteristics in terms of providing overall protection because it is the plastic with the highest spread between brittleness transition temperature and heat distortion temperature. This makes polycarbonates generally preferred materials in transparent armor composites. Unfortunately, polycarbonate and the other useful plastic materials useful in the practice of this invention are soft and easily abraded by the action of dirt and dust. Further, these materials are frequently adversely affected by solvents and cleaning solutions when used to remove dirt. Thus, if plastics are used as the inner layer of a transparent armor composite, cleaning the surface dirt and grime will inevitably cause scratching. This causes the optical properties to be adversely effected. The scratching can cause the transparency of the transparent armor composite to substantially degrade in under one year. The substantial degradation of transparency necessitates replacement of the composite. Since the transparent armor composites are expensive, frequent replacement creates a substantial financial burden on maintenance budgets.
It appeared the only alternative to a degrading composite was to have an innermost glass layer. This carries an increased spalling risk. The transparent armor assembly of the present invention provides a system with separate, parallel elements combined in a basic structure. The first element is a transparent armored composite that can defeat a penetrator and has an outer layer which withstands the abrasion of the ambient environment outside the vehicle. The second element is located between the first element and the vehicle""s interior, removed from the first element so that the shock of the penetrator is absorbed by the first element and is not transmitted to the second element. This structure allows the use of a sacrificial inner element which permits cleaning without degradation of the expensive portion of the structure while providing a good spall retaining to inner layer. As an added advantage, the second element of this invention is easily changed so we can easily switch from a heat limiting sun screen to a clear screen compatible with night vision devices. This allows enhanced daytime operation without adversely affecting nighttime operation
Briefly the present invention is an improved transparent armor structure for use in protecting an opening in a vehicle. The armor structure includes a multipart C-shaped frame mounted to a vehicle, the frame surrounding the opening. The frame is adapted to firmly hold a sheet of laminated transparent armor composite. The laminated armor composite has inner and outer layers of tempered silica glass material. The laminated armor composite has at least one layer of a polymeric material, such as polycarbonate, integrally bonded with the layers of tempered silica glass. The laminated armor composites useful in practicing this invention will comprise at least three layers integrally bonded to form a laminated bullet resisting structure. The bonding adhesives and other consolidating materials are chosen so that the composite is optically clear and non-yellowing. Of course, the laminated armor composite can be more than three lamellas thick. In constructing the laminated armor composite the various lamella are chosen from among assorted transparent materials chosen for their unique projectile resistance and flexibility characteristics.
The C-shaped frame that encloses the transparent armor composite is attached to the vehicle and extends into the vehicle interior. The C-shaped frame supports the transparent armor composite and associated parts of the structure in place. A y-shaped member is attached to the C-shaped frame, the y-shaped member being adapted to hold a freestanding transparent spall resisting layer parallel to and spaced from the innermost surface of the transparent armor composite. The y-shaped member is positioned on the inside of the vehicle and attached to the C-shaped frame in a manner to allow easily removal and replacement of the spall layer.
The spall layer can be formed from a transparent material generally chosen from the types of material used in the transparent armor composite. While the spall layer can be scratched, or otherwise adversely affected by cleaning solvents and abrasives, it can be easily and inexpensively replaced. The separation between the spall resistant layer and the transparent armor composite protects the spall resistant layer from shock waves induced in the transparent armor by penetrators. Also, having the spall resistant layer separately mounted and easily changed allows the spall resistant layer to have a sunshade or other optical coating suitable for daytime operation while allowing the spall resistant layer to be easily changed for nighttime operation.
A spacing means is located between the transparent armor composite and the spall resisting layer along their edges to form a chamber. The chamber contains a desiccant to minimize or eliminate the amount of moisture within the chamber so as to control any condensation, which would create an impediment to vision.